Archaeology was conducted in the Mill Field beginning in the 1980s. In 1984–1985, HSMC conducted a controlled surface collection of most of the Mill Field. This entailed plowing the field, gridding it into 10′ squares, and systematically collecting and mapping artifacts found on the surface. This phase of work determined that there were numerous important sites in the Mill Field, including Native American, early 17th-century, and late 17th-century components (Neiman et al. 1984). Based on this work, HSMC's then-Chief Archaeologist Dr. Timothy Riordan (1991) hypothesized that the remains of St. Mary's Fort might lie in the Mill Field.

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In 1992, with the support of a grant funded by the National Endowment for the Humanities and the hard work of students participating in the museum’s annual Field School in Historical Archaeology, HSMC visited the Mill Field again and excavated nearly 60 5×5′ units at the site. This work revealed a number of 17th-century artifacts and features, including evidence of blacksmithing and a robust palisade trench. However, the discovery and intensive study of the lead coffins buried in the Brick Chapel that year took precedence over further exploration. No further excavations were conducted in the Mill Field until 2019.

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HSMC excavated portions of the “traditional site” in the mid-1990s. In 1993–1995, areas of Town Center were surface collected and investigated via a limited shovel test pit survey (Miller et al. 2006). This work resulted in the recovery of early 17th-century artifacts on a bluff adjacent to a ravine that leads into Key Swamp—an ideal spot for a military fortification. This area had long been speculated to be the possible location of St. Mary's Fort (Forman 1938).

 

As both the Mill Field and the “traditional site” held promising evidence, the true location of the fort remained a mystery. However, the question of which site was correct was forced to take the back seat for decades as HSMC worked on many other important findings and construction projects, such as the research, excavation, and reconstruction of Cordea’s Hope, William Smith’s Ordinary, the Van Sweringen Site Exhibit, the Print House, and the Brick Chapel. These efforts also included the design and installation of the St. John’s Archaeological Site Exhibit and the Struggle for Freedom Exhibit in the Brome Slave Quarter, as well as the planning and execution of major mitigation efforts in preparation for the construction of buildings on the campuses of both HSMC and St. Mary’s College of Maryland, including HSMC’s new laboratory and archival facilities in Anne Arundel Hall and the Maryland Heritage Interpretive Center, the museum’s new Visitor’s Center (construction scheduled to begin FY2022).

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In 2017, Director of Research and Collections Dr. Travis Parno, decided to resume the search for St. Mary’s Fort. HSMC secured a Non-Capital Grant from the Maryland Historical Trust, with matching funds provided by the Historic St. Mary’s City Foundation for a new phase of exploration. The grant funds were used to hire expert geophysicist Dr. Timothy J. Horsley of Horsley Archaeological Prospection, LLC to conduct a geophysical survey of both the traditional site and the Mill Field. Dr. Horsley’s survey used three methodologies: magnetic susceptibility, magnetometry, and ground-penetrating radar.

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Magnetic susceptibility measures the level of magnetism to which soils are susceptible, a factor that can be increased by activities associated with human habitation such as burning and disposal of organic waste. This type of survey can reveal where humans have or haven’t lived in the past, but cannot detect specific cultural features or provide dates of occupation. The magnetic susceptibility survey revealed that most of both of the target sites had been occupied by humans at some point, but it did little to narrow down the search.

Magnetometry measures contrasts in magnetic susceptibility, as well as the presence of permanent magnetization. Permanent magnetization occurs when material is heated to a high temperature. Magnetometry is useful for identifying cultural features such as pits, ditches, and areas of burning such as hearths or kilns. The magnetometry survey revealed little at the traditional site. In the Mill Field, the magnetometry identified several anomalies that were likely hearths or kilns, as well as multiple pits related to late 17th-century occupation.

Ground-penetrating radar (GPR) entails projecting radar waves into the ground and recording where the radar reflects back off of subsurface anomalies. When conducted at a high resolution, GPR can identify buried cultural features (e.g., foundations, trenches, hard-packed floors, post holes) and geological anomalies (e.g., rocks and boulders) with a high degree of accuracy. The GPR survey revealed little at the traditional site, but in the Mill Field, it revealed a large palisaded enclosure, along with hundreds of other cultural features both inside and outside of the enclosure.

 

Inside the palisaded enclosure, the GPR survey identified numerous post holes, pits, and other features. Inside the northwestern and northeastern walls, lines of post holes are suggestive of defensive architecture such as firing platforms. Inside the southern corner, an arc of posts may have been part of an interior bastion or firing platform. In the western half of the enclosure, there are areas where linear arrangements of post holes indicate substantial English timber frame buildings once stood. In the eastern half, multiple circular clusters of post holes are suggestive of Native American structures.

The GPR survey also identified multiple late 17th-century structures and landscape features (e.g. fence lines, road ditches). These buildings are oriented along the road to the Mill, a road that was part of the late 17th-century Baroque town plan of St. Mary’s City.

 

Using the results of Dr. Horsley’s survey, HSMC archaeologists, led by Dr. Parno, conducted excavations in the Mill Field and definitively located portions of the ditch used to construct the palisade that originally surrounded St. Mary’s Fort (archaeologists call the process of conducting excavations to test geophysical survey results “ground-truthing”). The excavations also confirmed the presence of the curved bastion on the fort’s western corner. 

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Based on this new evidence, Dr. Parno and his team were able to both confirm the location and update the original rendering of what the fort contained. 

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Now that the location is confirmed, HSMC will continue seasonal excavations in the Mill Field to learn more about the construction and internal arrangements of St. Mary’s Fort. The museum will also continue to evaluate options for interpreting the findings in the Mill Field. In the meantime, while excavations are being conducted, the dig site is open to visitors with a museum ticket. Please see our website for further details.